Starting with your cylinders around arbitrary minor axes, for the most part your work here is headed in the right direction. I noticed that while you had some cases that definitely got too parallel (63, 65, 48, 32, 37, 16, 17, 21, 22, 1, 4, 11, 14, etc) these were concentrated more towards the beginning, and you appeared to be somewhat aware of it yourself (flagging it on 63, after which it didn't happen much).

I also noticed an improvement in your overall line quality as you progressed through the set, which suggests to me that you were taking more time and more care with your work. One thing that caught my eye is that as you worked through it, you appeared to be more and more and more aware of how the two ways in which an ellipse changes as we compare the end closer to the viewer and the end that's farther away. As we know, the degree will widen as we slide further back, and the overall scale of the ellipse will get smaller as well, giving us two "shifts". The thing that I don't explicitly spell out in the lesson material - as I want to give students the opportunity to pick up on this themselves, then explain it in my feedback - is that these two shifts operate together. Since they both convey the rate of foreshortening being applied to the form (in other words, how much of the length of the cylinder can be measured directly on the page versus how much exists in the "unseen" dimension of depth), they operate in tandem. The more the cylinder turns to point at the viewer, the less of its length can be measured directly on the page, leaving more of it to be conveyed through foreshortening, and so that would reflect in both changes to the ellipse.

Continuing onto the cylinders in boxes, your work here is by and large done fairly well. This exercise is really all about helping develop students' understanding of how to construct boxes which feature two opposite faces which are proportionally square, regardless of how the form is oriented in space. We do this not by memorizing every possible configuration, but rather by continuing to develop your subconscious understanding of space through repetition, and through analysis (by way of the line extensions).

Where the box challenge's line extensions helped to develop a stronger sense of how to achieve more consistent convergences in our lines, here we add three more lines for each ellipse: the minor axis, and the two contact point lines. In checking how far off these are from converging towards the box's own vanishing points, we can see how far off we were from having the ellipse represent a circle in 3D space, and in turn how far off we were from having the plane that encloses it from representing a square.

Ultimately it comes down to following the process as stipulated, and you've done that fairly well. I would advise you against particularly extreme boxes (like 236 and 241A/B) because they're going to throw off just how useful the line extensions end up being to you.

I also noticed that you forgot to apply some of the line extensions to a few of these- 241B, 246, 222, and that earlier in the set (like 157, 159, etc) you drew some of your boxes too parallel which also would have undermined the usefulness of the exercise. As long as you stick to having 3 concrete vanishing points with noticeable convergence, but avoid going too extreme with any aspect of the boxes, you should be well equipped to continue making good use of this exercise.

I'll go ahead and mark this challenge as complete.